In manufacturing operations involving the heating of a solid aggregate material to relatively high temperatures such as in the production of light weight aggregate or calcined limestone, the aggregate is typically processed in a rotary kiln having a horizontally extending rotatably mounted tubular body. Rotary kilns used for this purpose are typically quite massive, e.g. ten to twelve feet in diameter and fifty to a hundred feet or more in length. Because of the size of the rotary kiln and the fact that the entire tubular body thereof is mounted for rotation, the rotary kiln is quite difficult to insulate and consequently a considerable amount of the heat input to the kiln is lost through the walls thereof.
In an effort to increase the efficiency of a rotary kiln and reduce the fuel requirements, separate cooling devices have been developed for use at the discharge end of the rotary kiln for cooling the aggregate which is discharged from the kiln while transferring the heat content of the heated aggregate to the incoming air. Additionally, separate preheater devices have been developed for use on the input end of the rotary kiln for preheating the incoming aggregate by contact with the waste heated gases from the kiln.
In my copending application, Ser. No. 088,522, filed Oct. 26, 1979 and entitled APPARATUS AND METHOD FOR TREATING AGGREGATE MATERIAL WITH A FLOWING GAS, I have disclosed an improved apparatus and method for preheating solid aggregate prior to introduction to a rotary kiln. In accordance with the apparatus and method disclosed in this copending application, the aggregate is directed downwardly along a predetermined zigzag path of travel while being maintained in the form of a relatively thin layer and while the heated gases which are discharged from the kiln are directed upwardly along a predetermined sinuous path of travel repeatedly passing back and forth through the downwardly moving thin layer of aggregate from opposite sides thereof. This arrangement provides highly effective contact of the waste heated gases from the kiln with the aggregate, so as to preheat the incoming aggregate and effectively utilize the otherwise wasted heat content of the gases discharged from the kiln.
In my copending application Ser. No. 095,446, filed Nov. 19, 1979, and entitled APPARATUS AND METHOD FOR HEATING AN AGGREGATE MATERIAL, I have disclosed a related, but improved apparatus and method which provides for preheating the aggregate to a higher temperature prior to introducing the aggregate into a rotary kiln. In accordance with this application, supplemental heating means is provided within the pre-heater apparatus for further heating the waste heated gases which are discharged from the rotary kiln.
The aggregate preheater devices of my aforementioned copending applications are of simple and relatively inexpensive construction as compared to the devices previously known for this purpose, and provide for highly effective transfer of heat between the aggregate and the following gases.